The objective of this program is to understand the molecular mechanisms which are responsible for generating the first electrical signals used in visual information processing. The photoexcitation of purified vertebrate and invertebrate photoreceptor membranes will be studied in vitro. Biochemical techniques will be used to probe underlying membrane mechanisms and to specify the steps which occur during the transduction of light energy into a membrane polarization. The roles of purified membrane components, particularly the visual pigments, will be determined in dissociation and reconstitution studies.